1. Field of the Invention
This invention relates to a vaned stirrer to be used in molten metal of high temperature or the like, and more particularly to stirrer vanes formed of carbon-ceramics composite material which can sufficiently endure stirring operations in high temperature molten metals of 300.degree. C. to 1200.degree. C. or in other high temperature atmospheres.
2. Description of the Prior Art
Generally, when a metal such as aluminum is melted in crucibles or other containers, a temperature difference occurs between the center and peripheral portions of the containers. Therefore, rotary stir vanes of various shapes have been employed on such occasions in order to provide a more uniform temperature distribution. Further, similar rotary stirrer vanes are also necessitated when unformly admixing various substances into molten metals.
However, the conventional molten metal stirrers which have thus far been employed for these purposes are mostly of metallic vanes consisting of steel plates or the like, which tend to melt away gradually from their outer ends during rotation in molten metal of high temperature, giving rise to a problem that the stirring condition is changed upon time lapses. On the other hand, the stirring vanes which are formed of carbon are exempt from the melting problem, but they undergo considerable wear by aerial oxidation when lifted up from the molten metal after a stirring operation and are cooled in the air, which limit the repeated use of the vanes to a certain number of times. With regard to stirring vanes of ceramics alone such as aluminum oxide, there is a problem that the vanes are apt to be ruptured by thermal shocks when suddenly lifted up into the air from molten metal of high temperature due to the low resistance efficiency to thermal shock, in addition to the difficulty which is encountered in a machining stage due to the high hardness of ceramic materials. That is to say, there have not yet been developed molten metal stirring vanes which can endure long stirring operations.
Further, recently there is a trend that the industrial furnaces which are used for thermal treatment of metals or the like are operated at higher temperatures to enhance physical andC mechanical properties of products, for example, at high temperatures of 950.degree.-1250.degree. C. In addition, the furnaces of this sort are required to maintain a uniform temperature distribution in the processing atmosphere for quality control. Therefore, there has been a strong demand for heat resistant fans which can endure operation in such high temperature atmos- pheres.
However, the existing heat resistant fans are mostly of a metallic material so that they are limited to operations at temperatures up to 950.degree. C. at highest. Namely, at the present moment there are no heat resistant fans which can endure higher temperatures.